The present invention relates to the provision of services in augmentation of the standard communications service from a cellular wireless communications system. In particular, the mobile units of primary interest are cellular telephones, personal digital assistants, wireless-equipped laptop computers, and other similar devices equipped with wireless transceivers for normal operation under a “cellular” telephone system, such as those implemented in accord with the GSM, UMTS, CDMA, and TDMA standards and specifications.
An objective of the present invention is to provide the technology for enhanced automated control of the power transmitted by the wireless mobile communications units, so that the desired and required services can be effectively and accurately maintained, while also optimally conserving the energy available in the mobile units. In particular, the technology of the present invention provides the control of the mobile unit's transmitted signal power and/or duration in a manner to effect the reception of the transmitted signal at dynamically determined varying energy levels and/or multiple reception stations, for the enhanced performance of services that exploit the information obtained via enhanced signal energy or multi-site signal reception.
As realized and noted in the art for wireless communications systems, the control of a mobile unit's transmitted power is managed to accomplish sufficient signal reception at acceptable communications levels and/or at a single reception site. The intended single site is that of the serving cell, which cell is identified by its cell global identity (CGI). The power control objective for the management of the transmitted (Tx) power of the mobile station/user equipment (MS/UE) is to maintain sufficient received (Rx) signal power at the serving base transceiver station (SBTS) for acceptable wireless communications quality of service (QoS) or bit error rate (BER), while still minimizing the MS Tx power for reduced interference at neighboring (non-serving) cells and for reduced energy drain in the subject MS/UE. Thus the intent for the conventional Tx power control is to prevent energy drain exceeding that required for communications with the MS/UE and to prevent the possibility of multi-site interference reception, to the maximal extent possible.
Examples of the background art are available in the descriptions of the technology for various wireless communications systems. In North American Time Division Multiple Access (NATDMA) wireless communications systems, the MS/UE uses a maximal Tx power for its initial short-term access/control channel interactions with the SBTS, through which the MS/UE gains access to and is assigned the voice/traffic channel usage for its actual intended communications. At the initial onset of its usage of the voice/traffic channel or frequency band, the MS/UE may initially maintain its high Tx power to support SBTS power evaluation, but thereafter the SBTS commands the MS/UE to reduce its power to a minimal level that the SBTS evaluates is necessary for adequate communications QoS at its reception site. Since the reduced power level for the normal ongoing voice/traffic communications may be insufficient to support multi-site reception for those applications that require or benefit from such reception, the communications-centered Tx power management procedures often degrade or preclude the performance of associated or augmenting services. Such degraded service may include the wireless location service that supports the provision of location information to a public safety agent for response to an emergency call for help.
Another example of the background art for wireless transmission power control is presented in the descriptions of the technology for CDMA wireless communications systems. In North American Code Division Multiple Access (CDMA) wireless communications systems, the MS/UE initiates its transmissions at a minimal Tx power level above the background “noise” floor. If the MS/UE fails to establish connection with and response from its selected serving cell, the MS/UE progressively and incrementally raises its Tx power level until it reaches a level that is strong enough to obtain the necessary connectivity with its immediate SBTS. Thereafter, the SBTS aggressively, i.e., at a high repetition rate of signal quality evaluation and commanded re-configuration of the MS/UE Tx power parameters, manages the Tx power to maintain as precisely as possible the power that it (the SBTS) receives from the subject MS/UE and all other MS/UEs under its control. As with the TDMA transmissions, this communications power management is explicitly designed to achieve communications QoS only at the reception site of the serving cell, and otherwise is intended to minimize the associated “interference” level that would propagate from the subject MS/UE to any other neighboring cell sites. Again this logical communications-centered Tx power management approach is not conducive to or even supportive of the reception of adequate signal energy at multiple receiving sites for services that are adjunct to the communications service, but that require or would benefit from multi-site signal reception. (The CDMA air interface, as defined by EIA/TIA standard IS-95A (or its more recent version, i.e., CDMA 2000), is characterized by the use of both frequency and code separation. Because adjacent cell sites may use the same frequency sets, CDMA operates under very careful power control, producing a situation known as the near-far problem, thus making it difficult for most methods of wireless location to achieve an accurate location. (See U.S. Pat. No. 6,047,192, Apr. 4, 2000, Robust, Efficient, Localization System, for a solution to this problem.)
Although not described in sufficient detail for implementation, there have been previous “suggestions” for an overly simplified form for Tx power control in a wireless location system that augments a wireless communications system for emergency service response. Such suggestions were expressed in the publicly filed proceedings of the US Federal Communications Commission (FCC) over the course of its deliberations re Common Carrier (CC) Docket 94-102, which initially defined its Notice of Proposed Rulemaking (NPRM) to require wireless location support for emergency wireless communications in public mobile communications systems. In the 94-102 proceedings, including in the public's comments and reply comments, and in other related or associated documents, there have been a few expressions of the need to support multi-site signal reception for emergency wireless location determination through an infrastructure of location measurement units (LMUs). Based upon the realization that simultaneous multi-site signal reception is antithetical to the frequency sharing or reuse design of the standard public wireless communications systems, various suggestions for a simple, temporary power “spiking” for emergency calls were proposed to enable or enhance the infrastructure-based determination of the location of any wireless MS/UE involved in an emergency telephone call. Although such suggestions were not provided with any explicit descriptive teaching or exposition regarding how such power management should or could be implemented, the implied approach would support the required location determination through the use of a “maximum” Tx power level setting with a fixed maximal or unlimited time duration (i.e., the call duration) for the subject MS/UE.
U.S. Pat. No. 6,519,465 B2, Feb. 11, 2003, Modified Transmission Method for Improving Accuracy for E-911 Calls, describes that an E911 “trigger” may be stored in a phone and employed to cause the phone to transmit a special signal when the user dials 911. The special signal assists the WLS in locating the phone. See also, U.S. Pat. No. 6,463,290, Oct. 8, 2002, Mobile-assisted Network Based Techniques for Improving Accuracy of Wireless Location System. The '290 patent describes how the accuracy of the location estimate of a Wireless Location System is dependent, in part, upon both the transmitted power of the wireless transmitter and the length in time of the transmission from the wireless transmitter. Generally, higher power transmissions and transmissions of greater transmission length can be located with better accuracy than lower power and shorter transmissions. Recognizing that wireless communications systems generally limit the transmit power and transmission length in order to minimize interference within the communications system and to maximize the potential capacity of the system, several methods are described to meet the conflicting needs of both systems by enabling the wireless communications system to minimize transmit power and length while enabling improved location accuracy for certain types of calls, such as emergency calls. Such methods include mobile-assisted techniques in which the mobile unit includes functionality to assist in improving location accuracy. The WLS locates the mobile unit while the latter is using a modified transmission sequence comprising a message sent from the wireless transmitter using transmission parameters different from the normal transmission parameters broadcast on the forward control channel by the base stations in the associated wireless communications system. A trigger event, such as the user dialing 9-1-1, causes the mobile unit to operate in the mode in which the modified transmission sequence is used.
None of the background art suggestions for or descriptions of a dynamically adjusted Tx power level for the subject MS/UE integrate diverse sources of power-related information to evaluate and determine the optimal level and/or the optimal time (start and stop) duration for the Tx power of the subject MS/UE to enable accurate parametric characterization and/or multi-site signal reception. If the previously described pre-determined maximal power-level settings were to be routinely applied, the associated communication interference would be maximized at neighboring cell sites, and such interference would severely degrade the ongoing and subsequently ensuing communications that the communications system is intended to serve. Such Tx power management does not exploit the available real-time power-related information that could be used in an assessment of what signal power and duration could optimally serve the joint needs of minimal neighboring site interference and temporary multi-site location determination or enhanced signal parameter characterization. In fact, such an overly simplistic power-management approach for one MS/UE involved in an emergency communication would likely also interfere with the QoS performance for any other MS/UE attempting simultaneous or coincident emergency communications under the control of the same SBTS, let alone those MS/UEs operating under the interference-plagued control of neighboring cells. In order to mitigate the degradations in communications performance that can occur when a MS/UE transmits at an uncontrolled maximum power level, effective use of the current power-related information in the present invention can potentially optimize the performance of the communication system without precluding the signal characterization and/or source location determination associated with other augmenting system services.
In contrast with the background art, including that referenced above, the technology disclosed below integrates and exploits the information of various types, particularly real-time location- or distance-related measurements and measurements of currently received power, to support a selected MS/UE Tx power level that is derived to meet the specific immediate need for temporary enhanced-level and/or multi-site reception and signal parameter extraction. The inventive technology also enables and supports the “continuous” ongoing re-evaluation of the appropriate MS/UE Tx power level to the extent needed for the ongoing support of relevant services.